This invention relates to a woven fabric structure, partially in the field of papermachine clothing and other industrial belting, and particularly to structures contributing to the formation of a jointing seam in such a fabric for joining ends of the fabric to form an endless belt.
A common form of seam is achieved by extending selected longitudinal (machine direction) warp yarns of the fabric beyond the last transverse (cross direction) weft yarn, to form a loop, the end of which is back-woven into the fabric. The non-selected machine direction warp yarns are looped about the last cross direction weft yarn and the end back-woven into the fabric. Such a structure is described in GB-A-1488815, which discloses two patterns of weaving back the looped yarns, and cutting short of certain other MD yarns to provide space for the back woven loop ends.
Normally all the warp yarns have the same thickness or width, so that as a result when using only half the warp-yarns to form the loops, to afford space for interdigitation of the corresponding loops of the opposite end of the fabric, the tensile strength of the seam is relatively poor and there is a higher propensity in the seam region for marking of the paper sheet due to the greater open area in the seam region, as about 50% of the total width of the fabric is open space.
One approach to solving this problem is to use more than 50% of the warp yarns to form the loops. An example of this is WO 92/15743 wherein the problem of obtaining space for interdigitation of loops where more than 50% space is used by the loops of each side, is tackled by crossing adjacent loops over each other. However the use of more than 50% warp yarns, and the crossing of the looped yarns makes the already complicated, prolonged and expensive seaming process take even longer to carry out.
U.S. Pat. Nos. 5,503,196 and 5,769,131 describe a warp yarn system in a papermakers fabric comprising single wide tape-like yarns alternating with pairs of narrow yarns. The wide yarns are disposed with long floats and form an outer shell to protect the woven structure. These wide tape like yarns are, in U.S. Pat. No. 5,503,196 explicitly not used for seaming whilst U.S. Pat. No. 5,769,131 shows wide yarns from one fabric end being interdigitated with narrow yarns from the other fabric end, and the wide yarns are not used for seaming from both ends of the fabric.
An object of the invention is to provide a fabric structure which enables seaming to be carried with more than 50% of the warp yarn width, thus attaining lower open space in the seam, leading to a reduced propensity to marking of the paper sheet.
According to the invention a woven fabric structure comprises an array of warp yarns interwoven with an array of substantially orthogonally extending weft yarns using warp yarns of differing width, characterised in that said warp yarns comprise relatively wide warp yarns arranged in groups of two or more alternatively with relatively thin warp yarns arranged in groups of two or more and that said relatively wide warp yarns are extended in a seam region to provide seaming loops on each end of the fabric.
The fabric is preferably for papermachine clothing, such as a dryer fabric a forming fabric, extending nip press belt, press sleeve, basecloth, or for a filter belt or conveyor belt.
The warp yarns are preferably arranged in groups comprising alternating pairs of relatively wide yarns and pairs of relatively thin yarns. The alternating groups of warp yarns may each comprise single yarns, or any other number, and need not comprise the same of wider and thinner yarns in the respective groups.
In seaming the fabric, in order to effect a loop and pintle wire joining seam between the opposite ends of the fabric, the thinner yarns are preferably looped around the last weft yarn (extending parallel to the edge, across the width of the fabric), and the wider yarns are extended beyond the last weft yarn to form loops which are interdigitated with similar loops of the opposing fabric end, and joined by a pintle wire passed through the tunnel formed by the interdigitated loops.
The loops will, being provided by the wider yarns, comprise more than 50% of the width of the fabric.
The fabric may comprise a single layer woven construction, with all weft yarns in a single tier, however multi layer, or multi-weft tier fabrics may also be used.
The warp yarns, at least the wider yarns, are preferably flat yarns. The thinner yarns may also be flat yarns. However either or both the wider and thinner warp yarns may be of other cross-sectional profiles, such as triangular or semi-circular.
The invention also provides a method of seaming a woven fabric for forming the fabric into an endless belt the fabric being formed with an array of longitudinally extending warp yarns of differing widths, characterised in that the warp yarns comprise relatively wide yarns arranged in groups of two or more alternatively with relatively thin warp yarns arranged in groups of two or more, said relatively thin warp yarns being looped about a last weft yarn of the fabric edge, and the relatively wide warp yarns being formed into extended loops extending in the plane of the fabric beyond said last weft yarn at both ends of the fabric.
Preferably the seam is completed by interdigitating said loops with corresponding loops on an opposed end of the fabric, and passing a pintle or wire through said interdigitated loops.
The invention further provides an endless fabric formed by seaming by the method according to the invention, or comprising a fabric including a woven fabric structure according to the invention.